Bac­te­ria the likely cause of fish deaths

Pilbara News - - News - Tom Zaun­mayr

Re­cent fish deaths in Hamp­ton Har­bour are be­ing in­ves­ti­gated by the Depart­ment of Fish­eries, with nat­u­rally oc­cur­ring bac­te­ria top­ping the list of sus­pects.

While the DoF couldn’t con­firm the cause of five fish deaths re­ported last week, bio­di­ver­sity sec­tion leader Shaun Mered­ith said tri­chodesmium was com­mon at this time of year. “Blooms of the cyaonobac­terium tri­chodesmium oc­cur nat­u­rally and can de­plete wa­ter of oxy­gen, re­sult­ing in the death of fish when wa­ter tem­per­a­tures in­crease and winds and swells are light or there is lim­ited ‘flush­ing’ of a wa­ter body,” he said.

“It is con­ceiv­able if pe­ri­ods of low wind, swell and warm wa­ter com­bine that fish deaths from as­so­ci­ated anoxic con­di­tions could … oc­cur. At this time of year in Dampier, the sur­face slicks of tri­cho can col­lect in shel­tered bays, so … those bays are where you could ex­pect oxy­gen lev­els to drop.”

Mr Mered­ith said tri­chodesmium was re­spon­si­ble for the deaths in 1996 of farmed pearl oys­ters near Dampier.

The bac­te­ria’s pink-pur­ple and light green sur­face slicks can of­ten be mis­taken for co­ral spawn.

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